AEG Electrolux EWD 1409 I User Manual download pdf (Page 11)

Frequently Asked Questions answered by the DENSO technical team

Q1: What role do Lambda Sensors play?

A: In order to reduce emissions, modern cars have been designed

to carefully control the amount of fuel they burn. The Lambda (or

Oxygen) Sensor is a critical component in this process, Its goal is to

work together with the car’s fuel injection system, catalytic convertor

and electronic control unit (ECU) (Fig. 1) to achieve the lowest

possible output of environmentally harmful engine emissions.

The Lambda Sensor does this by monitoring the percentage of

unburned oxygen present in the car’s exhaust gases. This data is fed

to the car’s ECU, which adjusts the A/F (air/fuel) mixture. The correct

air/fuel mixture enables the Catalytic Converter to run efficiently.

This ‘exhaust gas cleaning system’ removes as many of the harmful

emissions as possible from the exhaust before it leaves the car.

Q2: Where are the Lambda Sensors positioned?

A: Every new car, and most cars manufactured since 1980, has a

Lambda Sensor. It is positioned in the vehicle’s exhaust pipe before

the Catalytic Converter, where it measures the oxygen present

in the exhaust gases and informs the ECU, enabling the ECU to

calculate what adjustments are needed to the air/fuel mixture. The

exact location of the Lambda Sensor varies according to whether the

vehicle has a V-type or In-line type exhaust system, and depending

on make and model. Some typical engine mounting configurations

are shown in the LOCATION section of this catalogue.

Q3: How exactly do Lambda Sensors work?

A: Lambda Sensors work together with the vehicle’s fuel injection

system, Catalytic Converter and engine management system or

electronic control unit (ECU) (Fig. 1) to help achieve the lowest

possible output of environmentally harmful engine emissions:

> The Lambda Sensor monitors the percentage of unburned oxygen

present in the car’s exhaust gases.

> According to whether the oxygen content in the exhaust gas is

too high (a lean mixture) or too low (a rich mixture) the Lambda

Sensor transmits a fast-changing, fluctuating voltage signal to the

ECU.

> The ECU responds to this information by adjusting the air/fuel

mixture entering the Catalytic Converter. The goal is to keep the

air/fuel ratio very close to the ‘stoichiometric’ point, which is the

calculated ideal ratio of air to fuel entering the Catalytic Converter.

Theoretically, at this ratio, all of the fuel will be burned using almost

all of the oxygen in the air. The remaining oxygen must be exactly

the right quantity for the Catalytic Converter to function efficiently.

> The Catalytic Converter then treats the exhaust emissions before

they leave the car. Most modern cars are equipped with a three-

way Catalytic Converter. ‘Three-way’ refers to the three regulated

(harmful) emissions it helps to reduce - Carbon Monoxide (CO),

unburnt Hydrocarbons (HC), and Nitrogen Oxide (Nox) molecules.

The exact amount of oxygen in the exhaust gasses is important

to the Catalytic Converter because it affects how well it is able

to remove these harmful emissions from the exhaust gases. The

right amount of oxygen enables a chemical reaction to take place

between the harmful gases and the oxygen, resulting in harmless

gases leaving the Catalytic Converter.

If the converter is working correctly, all the oxygen in the exhaust

gases will be consumed by this chemical reaction.

Fig. 1: Engine with Sensors and Catalytic Converter.

1. Fuel Injector

2. Pre Cat Lambda Sensor

3. Catalytic Converter

4. Post Cat Lambda Sensor

Lambda Sensors Lambda Sensors Q&A

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AEG Electrolux EWD 1409 I User Manual Page 11

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